Listening to the Song of the Sea at the Big Chico Creek Ecological Reserve

In October a year ago, four microphones were installed at Big Chico Creek Ecological Reserve (BCCER) as part of a National Oceanic and Atmospheric Administration (NOAA)-funded collaboration between the University of California, San Diego and California State University, Chico. The little-known research installation consists of microphones that are part of a larger network of microphones within the western United States that produce research on the source of the ocean sound in the eastern Pacific Ocean and that can be used to verify existing wave models.

Kristoffer Walker, geophysics project scientist, UC San Diego, is the lead project scientist. Jeff Mott, director of BCCER, and Brendon Armstrong, field support assistant (who passed away last summer), assisted Walker and his crew in installing the array of microphones and wiring. Armstrong maintained the system until this past summer.

Walker offered an analogy to help understand the sub-audible nature of the sound that the system is recording (in an article co-authored with Mott and published on the BCCER website and in “Inside Chico State”): “During the holidays around the dinner table a memorable moment is often shared by dipping your finger in your glass of wine and circling the rim until the glass starts to ‘sing.’ This singing occurs because the frequency of the vibrations created by your finger matches the ‘natural frequency’ of vibration for the wine glass. In this situation, this natural frequency is as easy for us to hear as a tone from a piano. The ocean is much larger than a wine glass. But it, too, has a natural frequency and sings when waves from one direction collide with waves from the opposite direction. Because wind is constantly creating waves throughout the world’s oceans, waves from different storms eventually collide thousands of miles away, creating the ‘song of the sea.’

“Humans cannot hear the song of the sea. The ocean’s natural frequency is simply too low for the human ear to detect. However, special microphones can listen to the ocean quite well. In fact, the ocean’s natural frequency is so low that these sensors can hear the ocean thousands of miles away, just as you can hear the low-frequency rumbling of thunder from distant lightning.

“Just as having two ears allows you to pinpoint the location of the ringing wine glass with your eyes closed, having more than one microphone allows scientists to locate where the ocean sound is coming from.”

The primary source of ocean wave forecasts, up until now, has come from NOAA forecasts from models created by measuring the height of waves inshore and offshore. Verifying the accuracy of these models is important because commercial and recreational human activities both near the coast and hundreds of miles off the coast rely on these models to make important decisions. Using the microphone system provides a way to verify the accuracy of the NOAA wave models without the prohibitive expense of placing the hundreds of thousands of buoys it would take to measure the waves. Since the wave-height models can predict where ocean sound will come from, the data from the project can verify that the NOAA wave models are accurate by comparing the observed sound locations to the predicted ones.

Preliminary results were presented at the American Geophysical Union meeting in San Francisco in December 2010. The microphones are still recording sound at BCCER, but the project may be in jeopardy due to a loss of funding from the NOAA, as the NOAA funding is determined by the approval of congress.

Mott’s role has been to direct resources at the array to fix problems and to be an advisor during the analysis of the data. His expertise on sources of sound in that region will help interpret the data, said Walker.

“The project with Kris and his crew from UC San Diego has been a wonderful experience,” said Mott. “The collaboration between universities shows that the Ecological Reserve system at CSU, Chico is not just an important local resource, but part of a broader system that is contributing to knowledge on a global scale.

“There are many people who assisted in this project. But we want to especially thank Brendon Armstrong. Brendon prepared BCCER for the microphones, helped install them, and was the primary caretaker. His dedication and hard work was critical to the success of this project, and we will miss him dearly.”

For more information on research into sub-audible sound, contact Kristoffer T. Walker, Institute of Geophysics and Planetary Physics, UC San Diego, at 858-534-0126 or visit his website at http://sail.ucsd.edu/~walker/.